1. Field of the Invention
The present invention relates to a video encoding method and apparatus and a video decoding method and apparatus with the use of a motion compensated prediction intra frame encoding.
2. Description of the Related Art
As a video compression encoding technique, MPEG 1 (ISO/IEC 11172-2), MPEG2 (ISO/IEC 13818-2), MPEG 4 (ISO/IEC 14496-2) are put to practical use broadly. These video encoding modes are performed by a combination of an intra frame encoding, a forward prediction intra frame encoding, an encoding and a bi-directional prediction intra frame encoding. The frames encoded by these encoding modes are called I picture, P picture and B picture. P picture is encoded using as a reference frame P or I picture just before the former P picture. B picture is encoded using as reference frame P or I picture just before and after the B picture. The forward prediction interframe encoding and bi-directional prediction interframe encoding are referred to as a motion compensated prediction interframe encoding.
When the video encoding data based on the MPEG mode is played back in fast-forward, a method that only I picture that the reference frame is not required is played back or a method that only I and P pictures is decoded while skipping B picture using a nature that B picture cannot be used as a reference frame is conventional. However, when only I picture is played back, if the period of I picture is long, a high-speed fast-forward playback can be carried out but a smooth fast-forward playback cannot be carried out. In a fast-forward playback with the use of I and P pictures, since P picture is encoded by an interframe prediction encoding, all I and P pictures must be decoded. For this reasons, it becomes difficult to change a fast-forward speed freely.
In the video encoding of the conventional MPEG mode, B picture is not used as a reference frame. Therefore, in case of the prediction configuration that plural B pictures continue, B picture must be encoded using P picture separating from B picture with respect to a time as a reference frame. This results in a problem that the encoding efficiency of B picture deteriorates. On the other hand, when the decoded B picture is used as a reference frame in P picture, it is necessary to decode all frames including B picture in the fast-forward playback while skipping B picture. As a result, it becomes difficult to perform the fast-forward playback effectively.
As described above, when the video encoded data obtained by the encoding including a motion compensated prediction interframe encoding such as MPEG is played back with a fast-forward, it is difficult to perform a smooth fast-forward playback at a free playback speed in playing back only I picture. When the fast-forward playback is performed with skipping B picture without decoding it, it is difficult to use the decoded B picture as a reference frame. For this reason, there is a problem that the encoding efficiency deteriorates in a prediction configuration that the B pictures continue.